Analysis of anion exchange membrane fouling mechanism caused by anion polyacrylamide in electrodialysis

• Mechanism of AEM fouling by APAM during ED is thoroughly analyzed.
• Voltage–time curves during ED processes are investigated.
• A gel layer is formed on diluate side of the AEM after fouling.
• AFM is utilized to investigate the interaction forces.
• Electrostatic interaction dominates the interactions between membranes and APAM.

Tertiary oil extraction technologies, especially polymer flooding, have been successfully used to enhance oil recovery, but the enormous amount of produced oily wastewater is urgent to be treated and reused. Electrodialysis (ED) is an important process in treating oily wastewater for reinjection. The aim of this work was to reveal the fouling mechanism of an anion exchange membrane (AEM) caused by anion polyacrylamide (APAM) in electrodialysis. Fouling experiments were carried out with different APAM concentrations at different current densities. Contact angle, electrical resistance and ion exchange capacity for the AEMs were measured to verify the fouling processes. The highest fouling phenomenon was observed with a higher APAM concentration at the current density close to the limiting value, which was indicated by evident increase of hydrophobicity and electrical resistance of the AEM. Morphology analysis by scanning electron microscopy (SEM) showed that a gel layer was formed on the diluate side of the fouled AEM and the ATR–FTIR spectra verified the presence of APAM on this side. Force–distance curves measured by atomic force microscopy (AFM) clearly confirmed that electrostatic interaction dominated the interactions between APAM molecules and ion exchange membranes.